Method and electrolyte for electroplating brass

ABSTRACT

An electrolyte and process for electrodeposition of brass from an aqueous alkaline cyanide bath containing zinc cyanide, copper cyanide and an additive of cyclohexanone resulting in a uniform color of deposit and elimination of streaks and nonuniformity in color.

United States Patent John A. Lisowskl;

Frank B. Lisowslti, both 0! Newport, Mich. 849,157

Aug. 1 l. 1969 Nov. 16, 1971 Natural Products Company Newport, Mich.

[721 Inventors [2 l 1 Appl. No. [22] Filed [45] Patented [73] Assignee[54] METHOD AND ELECTROLYTE FOR [50] Field of Search [56] ReferencesCited UNITED STATES PATENTS 3.440.152 4/1969 Lisowski et al.

Primary Examiner-G. L. Kaplan Attorney-Whittemore. Hulbert & BelknapMETHOD AND ELECTROLYTE'FOR ELEC'I'ROPIA'I'ING BRASS BACKGROUND OF'THEINVENTION The invention relates to the electrodeposition of brass andmore particularlyto brass alloy plating solutions which deposit ahigh-zinc alloy. it has been foundthat undercertain conditions theelectroplated surfaces have areas of different color with lines ofdemarcation which cannot be eliminated by-subsequent metal depositions.

This is particularly true in alkaline high-zinc brass alloy platingsolutions having metal ratios of 30 .to 45 percent copper and 70 to 55percent zinc. Under certain conditions of. cyanide and causticconcentrations, or under certain conditions of contamination, thedeposited brass alloys have different compositions on surfaces havingnonuniform current densities.

Usually, the zinc-rich deposit will be found in the low-current densityarea. This, at times, will create surfaces of different color, with thealloy highest in zincbeing a silver color, while the alloy withthe lowerconcentration remaining pink or yellow, and the interface having linesof demarcation which often cannot be erased by subsequent metaldepositions.

We have discovered a remedy which overcomes the abovementionednonunifonnity of the brass deposits and tends to promote more uniformdeposits free from discoloration and staining.

Our invention comprisesan additive for brass-plating solutionsconsisting of cyclohexanone. When cyclohexanone is used inconcentrations of 2 3 fluid ounces (80-90 'ml.) per thousand gallons ofplating solution up to the limit of solubility of cyclohexanone in thatsolution, a more uniform deposition is obtained over a wide currentdensity range. This results in a uniform color of deposit over theentire surface of the plated article.

A typical high-zinc brass plating bathhas the following analysis:

Ounces per Gallon Sodium cyanide (free) 8.00 Sodium hydroxide 5.00Copper cyanide 2.57 Copper as metal L80 Zinc cyanide 5.53 Zinc metal 3J0Cyclohexunone 0.002 Rariozcopper to zinc 36.8 to 63.2

The above brass-plating bath can be used with conventional brass anodescontaining zinc in the range of 55 percent to 60 percent and copper inthe range of 40 to 45 percent and an electrical current density of 30 to40 amperes per square foot.

in its broader aspects, the invention may be carried out with theingredients in the following wider ranges:

Ounces per gallon Sodium cyanide (free) 6.50 to 9.00 Sodium hydroxide2.50 to 6.00 Copper cyanide L4] to 4.23 Copper as metal L to 3.00 Zinccyanide 2.60 to 6.82 Zinc metal 1.45 to 3.80 Total zinc and copper 3.30to 5.40 Cyclohexanonc 0.002 to limit of solubility Ratio: Cu/Zn /70 to55/45 In practicing the invention, the cyclohexanone may be added to theplating solution in any convenient way to produce a true solution. Sincecyclohexanone has limited solubility in water and lower solubility inaqeuous solutions having high concentrations of electrolytes, directaddition of cyclohexanone to a brass-plating solution forms littledroplets over the surface which dissolve slowly. Therefore, work to beplated should not be introduced into the bath until the additive has hadan opportunity to dissolve as otherwise there can be skips in plating onthe surface of the parts being immersed for plating. In order to obtainmore rapid solution of cyclohexanone, in the plating bath, it isdesirable to first dissolve the cyclohexanone in solvents which aremutually soluble in cyclohexanone and the plating solution. Examples ofsuch solvents are formaldehyde, acetone, alcohols, diethylene glycolmethyl ether, etc. These tend to disperse the cyclohexanone for a largercontact with the solution.

If proprietary dry powder additives are regularly used to give a platingbath certain desirable properties, cyclohexanone can be blended withthese additives and introduced into the plating bath. This method willlikewise disperse the cyclohexanone for a more rapid solution.

The use of cyclohexanone in commercial brass plating depends somewhatupon the nature of the plating operations. if the conditions are suchthat uniform color quality is being obtained, then the addition ofcyclohexanone is unnecessary until such time as trouble appears. Ingeneral, it may be stated that the present invention is useful under twodifferent types of conditions. First, when the plating bath isrelatively free from contaminants and, second, when the platingoperations require the use of special additives as brighteners or forother purposes. Such additives sometimes hasten the deterioration ofcoior'uniformity and would therefore tend to make the plated articles ofinferior quality. When this occurs, it can be remedied by addingcyclohexanone in accordance with this invention. The present inventionis of great value when indium is added to brass-plating baths asdisclosed in U.S. Pat. No. 3,440,152, dated Apr. 22, 1969. Indium actslike a contaminant, but any detrimental effect on color uniformity canbe remedied by using cyclohexanone as set forth herein.

What we claim as our invention is:

l. A bath for electrodeposition of brass comprising an aqueous alkalinesolution of soluble compounds within the following ranges:

Ounces per gallon Sodium cyanide (lree) 6.50 to 9.00 Sodium hydroxide2.50 to 6.00 Copper cyanide l.4l to 4.23 Copper as metal 1.00 to 3.00Zinc cyanide 2.60 to 6.82 Zinc metal 1.45 to 3.80 Total zinc and copper3.30 lo 5.40 Cycloheunone 0.002 to limit of solubility Ratio: Cu/Zn30/70 to 55/45 2. A bath according to claim 1 in which the compounds arepresent in approximately the following amounts:

Ounces per Gallon Sodium cyanide (free) 8.00

Sodium hydroxide 5.00

Copper cyanide 2.57

Copper as metal L Zinc cyanide 5.53

Zinc metal 3. l 0 cyclohexanone 0.002

Ratio: copper to zinc 36.8 to 63.2

Ounces per gallon Sodium cyanide (free) 6.50 to 9.00 Sodium hydroxide2.50 to 6.00 Copper cyanide L4] to 4.23 Copper as metal L00 to 3.00 Zinccyanide 2.60 to 6.82 Zinc metal L45 to 3.80 Total zinc and copper 3.30to 5.40

Cycloheriarione 0.002 m limit of Iolubilily RatimCo/Zn 30/70 to 55/45Ounces per gallon Sodium cyanide (free) Sodium hydroxide Copper cyanideCopper as metal Zinc cyanide Zinc metal Cyclohexanone Ratio: copper tozinc

2. A bath according to claim 1 in which the compounds are present inapproximately the following amounts: Ounces per Gallon Sodium cyanide(free) 8.00 Sodium hydroxide 5.00 Copper cyanide 2.57 Copper as metal1.80 Zinc cyanide 5.53 Zinc metal 3.10 Cyclohexanone 0.002 Ratio: copperto zinc 36.8 to 63.2
 3. In the process of electroplating brass from anaqueous alkaline cyanide bath comprising zinc and copper in solution,the improvement in said pRocess of having cyclohexanone present insolution in an amount sufficient to prevent nonuniformity of deposits onsurfaces having nonuniform current densities.
 4. A process according toclaim 3 in which cyclohexanone is present in a concentration at least 2ounces per 1,000 gallons of solution.
 5. A process according to claim 3in which the plating bath is within the following ranges: Ounces pergallon Sodium cyanide (free) 6.50 to 9.00 Sodium hydroxide 2.50 to 6.00Copper cyanide 1.41 to 4.23 Copper as metal 1.00 to 3.00 Zinc cyanide2.60 to 6.82 Zinc metal 1.45 to 3.80 Total zinc and copper 3.30 to 5.40Cyclohexanone 0.002 to limit of solubility Ratio: Cu/Zn 30/70 to 55/456. A process according to claim 3 in which the plating bath hasapproximately the following composition: Ounces per gallon Sodiumcyanide (free) 8.00 Sodium hydroxide 5.00 Copper cyanide 2.57 Copper asmetal 1.80 Zinc cyanide 5.53 Zinc metal 3.10 Cyclohexanone 0.002 Ratio:copper to zinc 36.8 to 63.2